Generally, when light travels from a medium having a high refractive index to a medium having a low refractive index, light incident at angles greater than the critical angle is totally internally reflected. Consequently, in light-emitting devices such as organic electroluminescence light-emitting devices, a problem arises in which light is enclosed internally in the light-emitting device as a result of total internal reflection of light at the boundaries of layered materials. As a solution to this problem, a light-emitting device has been proposed which incorporates an optical sheet for extracting out light incident at angles greater than the critical angle.
For example, Patent Literature (PTL) 1 discloses an optical sheet formed by randomly arranging microscopic recessed and protruding structures. Incorporating this kind of optical sheet into a light-emitting device makes it possible to extract out light by diffusing light by diffracting at least a portion of light incident on the optical sheet at angles greater than the critical angle.